The invention relates generally to a method of electrically interconnecting electronic devices, more particularly, to a method of manufacturing an inkjet cartridge comprising a flex circuit having at least one cantilever lead and a printhead.
Electronic devices are used in a variety of common products. Typically, electronic devices are connected via wires and/or circuit traces. Many devices, however, such as inkjet cartridges, are sensitive to cost and have tight tolerance restrictions between components, necessitating a more advanced method of connecting and manufacturing electronic devices.
A typical inkjet cartridge has an electronic circuit wrapped onto two sides of a cartridge. The circuit connects the printhead on one (bottom) side of the cartridge to the rest of the printing device on an orthogonal side. To reduce the cost of the inkjet cartridge, it is desirable to reduce the size of this circuit. Typically the printhead is connected to the circuit on two sides of the printhead. One method to reduce the size of the circuit is to only connect to one end of the printhead, on the side closest to where the circuit wraps to the orthogonal side of the cartridge. The circuit need not span the length of the printhead or beyond in order to connect to the printhead.
One method to electrically connect to the inkjet printhead is known as wirebonding. The electronic circuit has a first plurality of bonding regions which are connected to a second plurality of bonding regions on the printhead via wires. Typically, the printhead and electronic circuit are positioned on a cartridge prior to wirebonding the two bonding regions.
Wirebond manufacturing of inkjet cartridges requires a flat bonding region on the circuit for proper adhesion. A bottom of form requirement in conventional printers requires the flat bonding region on the circuit to be in close proximity of where the circuit wraps to the orthogonal side of the cartridge. Bottom of form requirements are primarily determined by the position of a pinch roller and drive roller that drives the paper in relation to the inkjet nozzles on the printhead. A tight wrap of the electronic circuit (e.g. 0.5 mm radius) is required to meet bottom of form requirements.
The tight wrap causes great stresses in the circuit in the bonding region, so greater adhesion of the circuit to the cartridge is required to keep the bonding region flat. However, due to the reduction in the size of the electronic circuit on the printhead side of the cartridge, the area and leverage for adhesion of the circuit to the cartridge is much smaller than typical. Consequently the bonding region of the circuit is not flat and resultant stresses propagate to the encapsulant used to protect the wires.
Another such method of manufacturing an inkjet cartridge, known as tape automated bonding (TAB), also connects an electronic circuit to a printhead. The electronic circuit includes a plurality of leads which are bonded to a plurality of bonding regions on the printhead. Typically, both the printhead and electronic circuit are bonded together prior to being positioned onto the inkjet cartridge.
Similar to the wirebonding method, the TAB method includes a tight wrap required to meet bottom of form requirements, causing considerable stresses in the circuit near the plurality of leads. Greater adhesion of the circuit to the cartridge is required to counter the increased tendency of the circuit to detach from the cartridge due to the added stresses, yet the available area and leverage for adhesion is much smaller than typical. Inadequate adhesion leads to resultant stresses in the bonds between the plurality of leads and the bond pads on the printhead, causing failure of the bonds. These stresses also propagate to the encapsulant protecting the plurality of leads and bonds to the printhead, reducing its reliability.
Typically, the electronic circuit cannot be pre-formed with the proper bent region (e.g. prior to bonding), because the electronic circuit has to conform as close as possible to the cartridge periphery, which varies on a per part basis. For wirebonding, this variation harms the flatness of the circuit in the bonding region. For TAB, this variation harms the critical alignment of the printhead to the inkjet cartridge.
Hence, a need exists for a method of electrically interconnecting electronic circuits and manufacturing inkjet cartridges that permits a substantial reduction in the size of the circuit on the printhead side of the cartridge, meets tight manufacturing tolerances, and/or prevents resultant stresses in the electronic circuit.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above and other problems in the prior art.
According to one aspect of the present invention, a method of manufacturing an electronic device is provided comprising the steps of providing a circuit having at least one cantilever lead, providing a die having at least one bonding region, bonding the at least one cantilever lead to the at least one bonding region, and bending the at least one bonded cantilever lead. In a preferred embodiment, the at least one cantilever lead comprises a first material having a greater ductility than a second material of the circuit. More preferably, the first material comprises copper.
According to another aspect of the present invention, the method of manufacturing an electronic device further comprises a step of shrouding the circuit having at least one bent cantilever lead.
According to another aspect of the present invention, the method of manufacturing an electronic device further comprises a step of encapsulating the at least one cantilever lead.
According to another aspect of the present invention, the method of manufacturing an electronic device further comprises a step of preventing the at least one bent cantilever lead from contacting the die in a non-bonding region.
According to another aspect of the present invention, an electronic printing device is provided comprising a die, a cartridge, and a circuit positioned adjacent to the cartridge, the circuit having at least one cantilever lead bonded to the die. The at least one cantilever lead is bent to the die. Preferably, the electronic printing device is an inkjet cartridge.
According to another aspect of the present invention, the at least one cantilever lead comprises a first material having a greater ductility than a second material of the circuit. Preferably, the first material comprises copper. More preferably, the second material comprises a flexible film.
According to another aspect of the present invention, the printing device further comprises a capping shroud positioned over the circuit, the capping shroud providing a continuous capping surface around the printhead.
According to another aspect of the present invention, the printing device further comprises an encapsulant dispensed over the at least one cantilever lead.
According to another aspect of the present invention, the die comprises a hedgerow, the hedgerow preventing the at least one cantilever lead from contacting the surface or corner of the die.
According to another aspect of the present invention, the die comprises a printhead.
According to another aspect of the present invention, the circuit comprises a flex circuit.
According to another aspect of the present invention, a method of attaching electronic devices is provided comprising the steps of positioning a first circuit having at least one protruding contact on a second circuit, attaching the at least one protruding contact to the second circuit, and applying a force to one of the first circuit and the second circuit, such that the at least one protruding contact is deformed by movement of one of the first and second circuits. Preferably, the first circuit comprises a flex circuit.